Field of the Invention
This invention relates to an IC card and, more particularly, to a printed circuit on a circuit board which is embedded in the IC card and to circuit patterns of IC chips mounted on that circuit board.
FIG. 1 diagrammatically shows a plan view of an IC card 1 having an IC module 10 embedded in a card main body 1a.
FIG. 2 shows an exploded perspective view of the IC module 10. As shown in FIG. 2, a circuit board 100 has printed circuit patterns 110a and 110b respectively formed on an upper face 101a and a lower face 101b thereof. IC chips 103a and 103b having corresponding wire-bonding pads 104a and 104b are mounted on the upper face 101a and the lower face 101b, respectively. The IC chips 103a and 103b are die-bonded on die-bond areas 105a and 105b. Further, wire-bonding pads 106a and 106b for wire-bonding to the wire-bonding pads 104a and 104b of the IC chips 103a and 103b are also formed on both faces 101a and 101b respectively.
If the IC card is used as, for example, an information memory card, it is necessary to design the IC card so that the thickness is reduced and the memory capacity increased. Attempts have been made to satisfy these requirements and realize a low-cost card by mounting a plurality of IC chips on both sides of a circuit board, as shown in FIG. 2. However, if a pair of IC chips of the same type and same function are mounted on both sides of a circuit board, the printed circuit patterns 110a and 110b on the upper side 101a and the lower side 101b exhibit inverted patterns around the IC chips, as shown in FIG. 2.
For this reason, the dispositions of the bonding pads and the printed circuit patterns around the portions of the circuit board 100 on which the IC chips 103a and 103b are mounted need to be made independently with respect to the upper and lower sides. It is not possible to use a common circuit pattern for both sides. Therefore, if a plurality of IC chips are mounted on both sides, the printed circuit patterns become complicated, which obstructs high-density packaging. To attain an even greater memory capacity, it is necessary to use a multilayer circuit board such as a 3- or 4-layer board. This not only goes against the above requirements for reduction in thickness but also causes production costs to be increased.
Thus, the conventional type of circuit board for IC modules is unsatisfactory in that it cannot be designed to allow an increased packaging density of ICs having the same functions (of the same type) or reductions in thickness of the IC module and IC card since it is not possible to use common patterns together because the patterns on the two sides of the board differ from each other or are inverted with each other.